1. Technical Field of the Invention
The present invention relates to a motor controller and, more particularly, to a motor controller capable of performing a safe and highly reliable motor control in the case where a trouble arises particularly in a sensor for detecting a position or a velocity of the rotor of a synchronous motor.
2. Prior Art
In general, a controller for controlling a synchronous motor has been used conventionally to find the position and velocity of the rotor of a motor from information of a sensor mounted on the motor, that is, a feed back detector. In the case where signal from the feed back detector becomes abnormal due to a defect of the feed back detector, the motor becomes non-controllable since it is not possible to find the position and velocity of the rotor of the motor. Hence, the motor is stopped by being allowed to make a free running or by means of a brake mechanically mounted on a motor shaft.
Further, in addition to a velocity feed back detector, a velocity feed back detector for use of a velocity feed back loss detection is mounted on the motor, and the velocity is calculated by a motor controller from information from the respective velocity feed back detectors, and these velocities are compared, and if there arises any difference in the velocities, it is determined that either of the velocity feed back detectors is defective, and the velocity feed back loss is detected. After the velocity feed back loss is detected, a velocity control is performed, and the motor is stopped, by using velocity feed back signal from the velocity feed back detector in normal operation.
As described above, when there arises the defect in the feed back detector of the motor, with respect to a method of stopping the motor by allowing it to make the free running or by means of the mechanical brake, there is available the motor controller in which a plurality of feed back detectors are employed and these detectors are selected for use when the feed back detector is abnormal. However, such a method increases the number of feed back detectors and, accompanied with this increase, detection circuits and electronic switches are increased. As a result, comparing to the case of a single feed back detector, the number of parts is increased, thereby causing a problem in that the reliability of the parts is lowered. This finally leads to the lowering of the reliability of the whole controller and, further, causes a problem in that an installation area is increased and costs are driven up.
Further, in Japanese Patent Publication No. 2001-112282, there is disclosed the motor controller, comprising a synchronous motor, magnetic pole position detection means for detecting the magnetic pole position of the rotor of the synchronous motor, inverter control means for controlling an electric power to be supplied to the synchronous motor according to the magnetic pole position detected by the magnetic pole position detection means, sensor abnormality detection means for detecting the abnormality of the magnetic pole position detection means, and magnetic pole position estimation means for estimating the magnetic pole position, wherein, in the case where the abnormality of the magnetic pole position detection means is detected by the sensor abnormality detection means, the electric power to be supplied to the synchronous motor according to the magnetic pole position estimated by the magnetic pole position estimation means is controlled.
The sensor abnormality detection means for detecting the abnormality of the magnetic pole position detection means is constituted by a waveform processing portion, an UP DOWN counter, an address generation means, a commutation sensor (CS) edge detector, a CS abnormality detector, a magnetic pole position detector, a Z-phase abnormality detector, a Z-phase switch, and an A and B-phase abnormality detector.
A and B-phase signals which are sensor outputs of the magnetic pole position detection sensor, a Z-phase signal, and each signal of CS1 to CS3 signals, and each inversion signal of all these signals are inputted to the waveform processing portion, and are subjected to the waveform processing such as a waveform shaping.
The A and B-phase signals subjected to the waveform processing are counted by the UP DOWN counter, and are outputted to address generation means. Further, the CS1 to CS3 signals are outputted to a CS edge detector, a CS abnormality detector, and a magnetic pole position detector.
Moreover, the CS1 signal is transmitted to the counter. The Z-phase signal is outputted to a Z-phase abnormality detector, a Z-phase switch, and the counter.
The Z-phase signal detects whether or not a Z-phase pulse is generated based on a CS1 pulse by the Z-phase abnormality detector, and outputs a Z-phase abnormality signal. The A and B-phase signals generate a predetermined pulse signal for every one rotation of the motor. The number of pieces of the A and B-phase edges between CS edges is counted and, when the number of pieces deviates from a predetermined range, an A and B-phase abnormality signal is outputted. Further, the CS abnormality detector observes a state of the CS1 to CS3 signals, and outputs a CS abnormality signal when all the signals are “H” or “L”.
By so doing as described above, when the abnormality of the Z-phase signal, the A and B-phase signals, and the CS signals are detected, the motor is controlled according to the type of signals in which the abnormality occurs.
In such a motor controller, in addition to the feed back detector for detecting the position and velocity of the rotor of the synchronous motor, a CS signal detector for detecting a commutation signal is provided to detect a magnetic pole position of the rotor of the synchronous motor and, therefore, in the case where the detection functions of these detectors all become abnormal, there arises a problem in that all the references of a comparison to see whether it is good or bad cease to exist, so that the detection or judgment of the abnormality becomes absolutely impossible with a result that it is no longer possible to control the motor.
Hence, the object of the present invention is to provide a motor controller in which an electrical angle calculated from the signal outputted from the feed back detector and the electrical angle found from an induced voltage of stator windings are compared and, when it is determined that they are abnormal, a motor is controlled by an electrical angle estimated from the induced voltage of the motor.